Linear ball bearings serve the purpose of mounting shafts or the like such that these can be displaced in the longitudinal direction with respect to a stationary object, or of guiding objects on stationary axles in an axially displaceable manner. The balls which are situated in the first ball channel of each ball loop of the cage, mentioned in the introduction, of a linear ball bearing of the generic type bear directly against the shaft to be mounted, absorb the forces which load the shaft and transfer them to the carrying plate which covers the first ball channel on the outside and is supported for its part on the inner wall of a bore, into which the linear ball bearing is inserted. The first ball channel merges via the deflection channels into the second ball channel, in which the balls are returned to the first ball channel. The radially inwardly pointing opening of the first ball channel is generally narrower than the diameter of the balls, with the result that the latter cannot fall out to the inside. To the outside, the balls of the first ball channel are held by the described carrying plate which can be held, for example, by a snap action connection in corresponding recesses of the cage.
Different constructions have already been disclosed in order to prevent the balls from falling out of the second ball channel which is open to the outside and out of the adjacent deflection channels, in the case of the linear ball bearing which is assembled to form a component ready for installation and is fitted with balls. DE 197 08 370 A1 has disclosed configuring the carrying plates to be so wide that they in each case cover both the first ball channel and the second ball channel on the outside. In a first refinement which belongs to an older prior art, the carrying plates are configured in each case in one piece and are provided on the inner side with running grooves for the loadbearing balls, the non-loadbearing balls and the respectively deflected balls. Carrying plate profiles of this type are complicated and expensive to manufacture. In another exemplary embodiment of the abovementioned document, the carrying plates are configured in each case in two pieces, that is to say they comprise a carrying plate which is configured as a metal rail for the loadbearing balls and a covering plate which is configured as a plastic rail for the other sections of the ball raceway. The required expenditure for manufacturing two separate components and joining them together to form a supporting and covering plate arrangement also makes this solution expensive.
The carrying plates or supporting and covering plate arrangements of this known linear ball bearing are inserted in each case from the outside completely into corresponding recesses of the cage and are held via a snap action connection in such a way that they are flush with the outer circumferential face of the cage. This results in a comparatively high overall shape of the cage in the radial direction with a correspondingly large space requirement.
A further disadvantage of the known constructions is also seen in the fact that the load direction characteristics of the linear ball bearing are dependent on the accuracy of the alignment of the carrying plates in the cage and therefore on the manufacturing accuracy of the cage itself, which is generally not a precision component, with the result that the load direction characteristics are frequently insufficient.
Attempts have therefore already been made to avoid the described disadvantages by the cage, which has been fitted with the balls, being plugged into an outer sleeve which receives it completely, which outer sleeve absorbs the forces which act on the loadbearing balls and transfers the forces to the bore wall, and also covers the second ball channel for the non-loadbearing balls to the outside (EP 0 004 593 A1). Although linear ball bearings having outer sleeves are cheap to manufacture and also robust and in addition have satisfactory load direction characteristics, their disadvantages lie in their comparatively low accuracy, their moderate running quality and a low load rating on account of the absence of a running groove for the loadbearing balls. Moreover, high pressing forces are required for inserting the linear ball bearings into the respective receiving bore.